Rava Paul, Dvorak Tomas, Markelewicz Robert J, Hiatt Jessica R, Sternick Edward S, MacAusland Stephanie G, Huber Kathryn, Wazer David E, Hepel Jaroslaw T
Department of Radiation Oncology, Tufts Medical Center, Boston, MA 02111, USA.
Brachytherapy. 2012 Sep-Oct;11(5):402-7. doi: 10.1016/j.brachy.2011.08.004. Epub 2011 Oct 12.
Advantages for electronic brachytherapy (EBT) of the vaginal cuff include decreased physical dose to the bladder and rectum. Here we compare (192)Ir with EBT using biological effective dose (BED) to account for the different radiobiological effectiveness (RBE) predicted for low-energy x-rays.
Fifteen data sets from five consecutive postoperative endometrial cancer patients treated with EBT were analyzed. Treatment planning was performed using PLATO software. The dose was prescribed as 21Gy in three fractions to a depth of 0.5cm. Physical dose, BED(3), and BED(10) were evaluated for the mucosa, bladder, and rectum. An RBE value of 1.5 was used for BED calculations.
Mucosal physical dose is 28.4% greater with EBT (36.6 vs. 28.5Gy, p<0.05). However, the BED(10) is increased by 79.1% (55.6 vs. 99.6Gy, p<0.05) and the BED(3) by 71.5% (118.8 vs. 203.7Gy, p<0.05). The physical dose (dose to 50% volume of the organ) to the bladder (9.3 vs. 6.6Gy, p<0.05) and rectum (7.2 vs. 4.2Gy, p<0.05) are reduced with EBT. BED(3) to the rectum and bladder are also reduced but to a lesser extent (13 vs. 8.3Gy, p<0.05; 18.9 vs. 14.7Gy, p=0.06, respectively).
BED takes into account the higher RBE of low-energy photons generated with EBT and provides a more accurate estimate of the biological effect. When using EBT, physical dose may underestimate the biological effect on the vaginal mucosa and overestimate the benefit for the bladder and rectum. Dose adjustment for EBT based on BED should be considered.
阴道断端电子近距离放射治疗（EBT）的优势包括减少对膀胱和直肠的物理剂量。在此，我们使用生物等效剂量（BED）比较铱-192（¹⁹²Ir）与EBT，以考虑低能X射线预测的不同放射生物学效应（RBE）。
分析了连续5例接受EBT治疗的子宫内膜癌术后患者的15组数据。使用PLATO软件进行治疗计划。剂量规定为分3次给予21Gy，深度为0.5cm。评估了黏膜、膀胱和直肠的物理剂量、BED(3)和BED(10)。BED计算使用的RBE值为1.5。
EBT的黏膜物理剂量高28.4%（36.6对28.5Gy，p<0.05）。然而，BED(10)增加了79.1%（55.6对99.6Gy，p<0.05），BED(3)增加了71.5%（118.8对203.7Gy，p<0.05）。EBT使膀胱（9.3对6.6Gy，p<0.05）和直肠（7.2对4.2Gy，p<0.05）的物理剂量（器官50%体积的剂量）降低。直肠和膀胱的BED(3)也降低，但程度较小（分别为13对8.3Gy，p<0.05；18.9对14.7Gy，p = 0.06）。
BED考虑了EBT产生的低能光子的较高RBE，并能更准确地估计生物学效应。使用EBT时，物理剂量可能低估对阴道黏膜的生物学效应，高估对膀胱和直肠的益处。应考虑基于BED对EBT进行剂量调整。
